The lutein is one kind of the oxy-carotenoids (called the xanthophylls) and is abundant in fruits and green vegetables, such as broccoli, Brussels sprouts, cabbage, kale, spinach, green beans, lima beans and lettuce, and in flowers, such as the marigold flower. Similar to other carotenoids, the lutein has been studied extensively as an antioxidant for the prevention of cancer and for other health benefits. Medical researches show that lutein and zeaxanthin reduce the age-related macular degeneration of the human body. (See, e.g., Seddon et al., J. Amer. Med. Assoc., 272 (18): 1439-1441, 1994.) The lutein has strong antioxidant capabilities in the human body and the macular degeneration prevention effects of lutein have made it a popular nutritional supplements and pharmaceuticals. Therefore, the FDA also considers lutein as a pharmaceutical. According to the standard requirement of the 30th ed. United States Pharmacopeia, to be qualified as a pharmaceutical the total carotenoids content of a product shall not be less than 80%, with the lutein content of not less than 74% and the zeaxanthin content of not more than 8.5%.
Many researchers have reported the process for the saponification, separation and purification of lutein from marigold flower extracts. The petal of the marigold flower is one of the excellent sources of lutein that exists naturally in the esterified form, as esterified with fatty acids such as the palmitic acids, the lauric acids and the myristic acids. In the conventional art, to produce the lutein crystals from the petals of the marigold flower, at first the marigold flower petals are extracted to obtain an oleoresin, with the n-hexane as the extract solvent. In general, the oleoresin so obtained contains only about 5% to 30% lutein ester. The oleoresin needs to be saponified, separated and recrystalized to obtain the lutein crystals. Usually, the process includes mixing the oleoresin with an alcohol solvent, followed by adding an aqueous or alcoholic solution of alkali into the solution. Thereafter, the solution is maintained at high temperatures until the oleoresin is completely saponified. After the saponification, the solution is diluted in a great amount of deionized water. The diluted solution is then separated in a high-speed centrifugation process using a centrifuge. Collect the solid so obtained and rinse the solid in deionized water and organic solvents to purify. Wet lutein crystals are obtained and are dried in a vacuum environment to obtain the dry crystals of lutein.
Several approaches in the purification of the carotenoids from plant extracts have been disclosed. Khachik (U.S. Pat. No. 5,382,714) disclosed a process for obtaining lutein and zeaxanthin from the marigold oleoresin. Here, the marigold oleoresin is mixed with a 45% aqueous solution of potassium hydroxide and saponified at 65° to 70° C. for about a half hour. The resulted crude lutein was about 70% pure is measured by a spectrophotometer. The crude lutein is then purified in a solvent containing dichloromethane and hexane to obtain lutein crystals of 97% purity. The disadvantages of this approach include that fact that the dichloromethane used in the purification process would reside in the resulted products.
Ausich (U.S. Pat. No. 5,648,564) developed a process for obtaining lutein crystal compositions containing approximately 79% total carotenoids and 73.6% pure lutein. In this invention, the marigold oleoresin is first mixed with 1,2-propanediol and saponified in a 45% alcoholic solution of potassium hydroxide at 70° C. for 10 hours. The saponified oleoresin is diluted in deionized water. Thereafter the lutein crystals so obtained are collected by using a centrifuge and washed in deionized water at 85° C. The drawbacks of this invention include: Saponifying the marigold oleoresin a high temperature for a long period of time would decompose the lutein. The high-speed centrifugation process is costly and increases the separation costs. In addition, the total carotenoids content and lutein content obtained are only 79% and 73.6%, respectively.
Rodriguez (U.S. Pat. No. 6,329,557) disclosed a process in which the saponified oleoresin is dispersed in water, adjusting the pH value of the suspension to 6 with phosphoric acid or acetic acid and maintaining the temperature of the suspension at 60 to 70° C. for 20 to 30 minutes. After that, the oily material is washed three or more times with an acid aqueous solution in organic solvents, such as hexane and heptane. The crystals are collected by filtration and centrifugation. This invention, however, uses a great amount of water and organic solvents and is hazardous to the environmental.
Madhavi (U.S. Pat. No. 6,380,442) mixed marigold oleoresin with iso-propanol and heated the mixture to 60° C. to obtain a free-flowing solution. After that, potassium hydroxide is added and the composition is maintained at the temperature of 60° to 65° C. for 90 minutes to saponify. The saponified oleoresin was diluted in deionized water. After the centrifugation of the solution, fine crystals are collected. The resulted composition has the total carotenoids and lutein contents of 95% and 90%, respectively. Like in the case of the Ausich invention, the disadvantages of this invention are that the high temperature in the saponification would decompose the lutein and that the high-speed centrifugation process in separating the crystals increases the costs of the process.
Kumar (U.S. Pat. No. 6,743,953) used iso-propanol as the solvent to saponify the marigold oleoresin at 70° C. for 3 hours. After that, the iso-propanol solvent is distilled off and the solids are collected, mixed in water by stirring and extracted three times using ethyl acetate. The ethyl acetate in the collected solution is then washed with water and distilled off. Finally, the residual solid is purified with hexane/acetone solution and washed with methanol. The total carotenoids content of the products is 86.23%, as determined by a UV/Vis spectrophotometer, and the total lutein content is 91.43%, as determined by HPLC analysis. Although this method produces highly purified lutein, the process is complicated and time consuming and requires large quantity of solvents and energy.
Recently in the U.S. Pat. No. 7,271,298, Xu proposed a process to improve the purity and the yield rates of the xanthophylls crystal. However, the disadvantages of this process are that the process is performed under high temperatures and that the high-speed centrifugation is required.
In most conventional arts, the main disadvantages are: The process is conducted under higher temperatures, which tend to decompose the lutein. The high-speed centrifugation is required, resulted at higher costs of the process.
It is thus necessary to develop a simplified method for the purification of carotenoids from plant extracts.
It is also necessary to provide an inexpensive method for the purification of carotenoids from plant extracts.
It is also necessary to provide a new method for the purification of carotenoids from plant extracts to obtain higher carotenoids contents.
It is also necessary to provide a method for the purification of carotenoids from plant extracts, wherein the solvents used are environmental.
It is also necessary to provide a method for the purification of carotenoids from plant extracts, wherein the process may be conducted under relatively low temperatures.
It is also necessary to provide a method for the purification of carotenoids from plant extracts, wherein the high-speed centrifugation process is not needed.